1. Field of the Invention
The present invention relates to a light source device and a projector provided with the light source device.
2. Description of the Related Art
Nowadays, data projectors are often used as image projecting devices for projecting images, such as displays of personal computers, video images and, images of image data stored in memory cards, on screens. Each of these projectors gathers light projected from light sources on a micromirror display device called a digital micromirror device (DMD®) or a liquid crystal display panel, to display color images on a screen.
Heretofore, in this type of projector, a discharge lamp having a high luminance has been mainly used as a light source, but in recent years, there have been made developments and suggestions of employing a light emitting diode, a laser diode, an organic EL or a fluorescent material as the light source. For example, in Jpn. Pat. Appln. KOKAI Publication No. 2011-13320, a light source device has been suggested which emits blue light obtained by dispersing an excitation light from a laser light source for emitting the excitation light having a blue wavelength, red light from a red color emitting diode for emitting the red light, and green light from a fluorescent material for emitting the green light by receiving the excitation light from the laser light source. In this light source device, a dichroic mirror is used which can transmit or reflect an arbitrary wavelength, to synthesize the blue light, the green light and the red light from the respective light sources on one image display device.
In the dichroic mirror disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2011-13320, the light can be synthesized with a high efficiency, if each wavelength of the synthesized light is a single-wavelength or a narrowband wavelength. However, when a light having an extensive wavelength distribution is synthesized, a portion of the wavelength bandwidth is not synthesized sometimes to cause a loss.
FIG. 1 shows an example of a light emitting distribution of a yttrium.alminum.garnett (YAG) fluorescent material which can be utilized as a light source for the green light. As shown in the drawing, on the short wavelength side of the light emitting distribution of the fluorescent material, any light emitting component is not present in a wavelength bandwidth of about 440 nm to about 460 nm which is used in a blue light source. On the other hand, on the long wavelength side, the light emitting component is present in a wavelength bandwidth of about 620 nm to about 640 nm which is used in a red light source.
In synthesizing the red light and the blue light with the light emitted by such a fluorescent material, the synthesis is possible by use of a dichroic filter having characteristics of reflecting the light of 500 to 600 nm at a 45° incidence and transmitting wavebands of the red color and the blue color, for example, as shown in FIG. 2. In a transition wavelength bandwidth having the reflecting and transmitting characteristics of the dichroic mirror which synthesizes the light having wavelengths by use of such a dichroic filter, the characteristics are usually moderately varied in a wavelength width of 30 to 40 cm, in consideration of costs and manufacturing yield. Therefore, when the emitted light from the fluorescent material shown in FIG. 1 is synthesized with the red light and the blue light by use of the dichroic filter shown in FIG. 2, a reflectance gradually deteriorates from about 580 nm, and most of the light emitting components of 620 nm or more are transmitted, with the result that the synthesis with the red light and the blue light is not accomplished. Accordingly, in this example, about 7% of the emitted light from the fluorescent material is not synthesized unnecessarily.